Two styles of U mineralization are associated with the Nonacho Basin: early U of the Hope Occurrence (northern basin) is disseminated in quartz-biotite-albite basement breccia, whereas later vein-hosted and disseminated U occurs in basement granitoids and basinal siliciclastics near MacInnis Lake (south-central basin). Although separated by 50 km, the two areas are connected by a series of north-east trending structures.
Extensive albitization precedes U at both Hope and MacInnis. At Hope, milled albitized-oligioclase clasts are surrounded by flood-quartz and biotite stockwork. Coarse-grained, Pb-rich U forms overgrowths on metamict zircon with biotite. High Ca, Al, Eu2+/Eu3+, and Ce3+/Ce4+ in zircon records reducing, albitization-related fluids. K-feldspar reaction rims between U and biotite indicate relatively high-T environment. Late molybdenite with chlorite locally overprints biotite. Pseudomorphs of biotite by muscovite with thorite may indicate dissolution of early U by lower-T, acidic fluids.
At MacInnis, fine-grained, Pb-poor U mineralization (+hematite, sericite) commonly forms overgrowths on earlier, partially dissolved Cu-sulphides (i.e. bornite, chalcopyrite) and rutile (± magnetite, K-feldspar and apatite). Coeval hematite and U on sulfides may record redox reactions for U mineralization. MacInnis U may ultimately be derived from early U occurrences, such as Hope, which were remobilized by fluids along regional faults.